Concrete is generally used within the industry to refer to a mixture of cement, sand, stone, and water which upon aging turns into a hardened mass. The term concrete, as used in the specification and claims herein, means not only concrete as it is generally defined in the industry (cement, sand and stone), but it also means mortar (cement, sand and water) and cement (cement and water which hardens into a solid mass upon aging).
In the construction field, after a batch of concrete has been produced for use at a particular site, it is useful to be able to obtain data concerning certain performance characteristics such as the in-place strength of the batch, maturity, and other characteristics. Accurate prediction of concrete performance can increase the quality of the end product, and can provide other benefits such as allowing the use of accelerated construction schedules.
Several methods for testing and monitoring in-place strength of a concrete mass have been incorporated into the American Standard Testing Methods, including ASTM C805 (The Rebound Number Method—the so-called Swiss Hammer Method), ASTM C597 (The Pulse Velocity (Sonic) Method), and ASTM C900 (The Pullout Strength Method).
In accordance with standards set forth in ASTM C31 (Standard Practice for Making and Curing Concrete Test Specimens in the Field), the compressive strength of concrete is measured to ensure that concrete delivered to a project meets the requirements of the job specification and for quality control. In order to test the compressive strength of concrete, cylindrical test specimens are cast in test cylinders and stored in the field until the concrete hardens.
In accordance with the standards, typically 4×8-inch or 6×12-inch test cylinders are used, and the concrete specimens are stored in a carefully selected location for a predetermined period of time. When making cylinders for acceptance of concrete, the field technician must test properties of the fresh concrete including temperature, slump, density (unit weight) and air content.